1. Field of the Invention
The present invention relates to sealing gaskets suitable for use in hard disc drive units and methods of manufacturing the same.
2. Description of the Prior Art
As is well-known, a sealing gasket is used in a hard disc drive unit to hermetically seal a pair of metallic casings of the unit with each other.
Sealing gaskets made solely of an elastomeric material are difficult to handle and precisely position during assembling operations of the units because the elastomer material forming the gaskets is not self-sustaining and freely deformable.
To obviate these drawbacks, Japanese Patent Kokai Publication No. 4-341986 proposes a gasket having a resilient sealing member supported by a rigid support plate or substrate. As shown in FIGS. 1 and 2 of the accompanying drawings, the gasket 1 includes a support plate 2 made, for example, by stamping of a sheet metal. The support plate 2 is provided with a central opening or cutout 3 and is properly trimmed in conformity with the contour of the unit casings to be sealed. An annular sealing member 4 of an elastomeric material extending along a desired sealing line is bonded to or otherwise properly affixed to the support plate 2.
The gaskets 1 shown in FIGS. 1 and 2 may be made by using the conventional injection molding or transfer molding techniques by placing the support plate 2 in a cavity formed in a mold and injecting an uncured elastomeric molding composition into the cavity, followed by curing of the molding material.
The mold is provided with gatings to the cavity to permit injection of the uncured molding material into the cavity, as is well-known in the art. When molding is completed and the molded product is rejected out of the mold, a part of the cured molding material initially filling the gatings necessarily remains on the molded product. Such residual materials resulting and deriving from the presence of the gatings will be referred-to herein as xe2x80x9cburrsxe2x80x9d, xe2x80x9cflashesxe2x80x9d or xe2x80x9cgate residualsxe2x80x9d.
In one type of mold, the gatings to the cavity are arranged in the form of sprue gates which open into the cavity in a direction perpendicular to the parting plane of the mold. The presence of such sprue gates gives rise to the formation of burrs projecting from the sealing member 4 in the axial direction, as shown at 5 in FIG. 2. The formation of the axially projecting burrs 5 is undesirable since they impair the sealing capability of the gasket if brought into contact with the casings of the hard disc drive unit. Accordingly, the gaskets as molded must be subjected to deburring operations to remove the undesirable burrs 5 deriving from the gatings. This results in an increase in the production costs. In addition, the deburring operation may occasionally damage the surface of the sealing member.
To eliminate the formation of the axially projecting burrs, another type of mold has been used in which the gatings to the cavity are arranged in the form of film gates which are located inwardly of the cavity to open into the cavity in a direction parallel to the plane of the gasket.
An example of the gasket molded by this type of mold is shown in FIGS. 3-6. As shown, the gasket similarly includes an annular sealing member 6 of elastomer supported by a support plate 7 of sheet metal having an inner aperture or cutout 8, the sealing member 6 being likewise arranged to extend along the inner periphery of the support plate 7.
However, the use of the mold provided with the film gates extending inwardly from the cavity would, in turn, result in the formation of flashes or film-shaped gate residuals 9 which extend inwardly beyond the inner periphery of the support plate 7 as shown by the ghost line in FIGS. 3 and 5, there being shown in FIG. 3 four such flashes 9 corresponding to the number of the film gates.
Formation of the flashes or residuals 9 still involves a certain problems. First, the flashes 9 must be removed very carefully by deflashing operations since the flashes projecting inwardly of the gasket into the inside of the unit casings may adversely affect the operation of the hard disc drive unit. The need for the deflashing operations substantially adds to the labor and time of manufacture.
Another disadvantage is related to the axial dimension or thickness of the film gates. More specifically, deflashing is carried out by moving a scraper blade along the inner edge of the support plate. By scraping with the scraper blade, the flashes or residuals 9 will be partly torn off from the molded product so that narrow residual segments 10 of the flashes 9 will be left on both sides of the finished gasket as shown in FIGS. 5 and 6. To permit or facilitate deflashing operations, the axial dimension of the film gates is preferably limited such that the axial thickness of the residual segment 10 is less than about 0.1 mm. As the residual segment 10 could not be bonded to the support plate 7 because it is preferable not to use an adhesive tending to issue any gaseous contaminants, there is a risk that the residual segments 10 having only a limited thickness are inadvertently torn off and separated from the sealing member 6.
As will be readily understood, in order to avoid crushing of the read-write heads and damage to the storage medium, sealing gaskets for use in hard disc drive units are subject to extremely strict quality requirements in that release or detachment of solid contaminants is absolutely prohibited.
Accordingly, it is an object of the present invention to provide a method of manufacturing a gasket which does not impair the operation and function of a hard disc drive unit and which provides an improved sealing capability.
Another object of the invention is to provide a method of manufacturing a gasket which is specifically designed to prevent separation or release of material forming the gasket.
A still another object of the invention is to provide a method of molding a gasket which method is capable of eliminating or minimizing the need for finishing operation such as deflashing and deburring.
This invention provides a method of molding an annular gasket by injecting or transferring an uncured elastomeric material into an annular cavity of a separable mold through a plurality of injection gates communicated with the cavity, followed by curing of the material.
The feature of the invention is that the injection gates formed in the mold are arranged radially outwardly of the cavity to ensure that, in the gasket as molded, any flashes or burrs resulting from the presence of the injection gates are formed radially outwardly of the gasket.
As in this manner any flashes or burrs that may be formed due to the presence of the injection gates are situated radially outwardly of the gasket, there is no risk that these flashes or burrs project inwardly of the gasket toward the inside of the casings of the hard disc drive unit in a manner to interfere with the internal component parts of the unit. Accordingly, deflashing or deburring operations after molding may be omitted altogether or more or less simplified.
Furthermore, should it happen that segments of these flashes or burrs are torn off or separated from the gasket for any reasons, such separation would occur outside of the unit casings so that the detached segments would never affect the operation of the internal components.
In a preferred embodiment of the invention, each of the injection gatings includes a film gate extending parallel to a parting plane of the mold to communicate with the cavity and a sprue gate extending perpendicular to the film gate to open into the film gate.
With this arrangement, when a cull is pulled and separated from the mold after curing of the molded material, the cull will be snapped or torn off from the gasket at some point in the sprue gate. This is advantageous in that deburring operation for removing the burrs deriving from the sprue gates can be omitted.
In a preferred embodiment, the gasket is made of an annular support plate made of a self-sustaining material such as metal and plastics, and of an annular sealing member of an elastomeric material affixed to and supported by the support plate. The film gates are provided at least on one side of the support plate. Preferably, the dimension of the film gates as measured perpendicular to the parting plane of the mold is equal to or larger than about 0.2 mm, preferably about 0.3 mm.
By using the film gates having an increased axial dimension, the thickness of the flashes resulting from the film gates is increased. This considerably increases the mechanical strength of the film gate flashes to permit the flashes to inseparably and securely adhere to the sealing member.
In another preferred embodiment of the method according to the invention, the mold cavity is so shaped that the sealing member is formed of a pair of symmetrical sealing beads disposed on both sides of the support plate. The support plate is provided with a plurality of through-openings.
Upon injection of uncured elastomeric material into the cavity followed by curing, the sealing beads on both sides of the support plate will be connected with each other by elastomeric material filled in the through-openings. This advantageously permits the sealing beads on both sides of the support plate to be securely affixed to the support plate without recourse to the use of an adhesive that would otherwise evolve gaseous emission.
In another aspect, this invention provides a method of molding a gasket having an annular elastomeric sealing member affixed to a support plate, the sealing member including a pair of symmetrical sealing beads disposed on both sides of the support plate, each of the sealing beads including inner and outer sealing lips radially spaced apart from one another. The injection gates are arranged to open into the cavity at a location situated radially outwardly of the inner sealing lip.
By arranging the injection gates at a location situated radially outwardly of the inner sealing lip, any flashes or burrs resulting from the injection gates will be formed radially outwardly of the inner sealing lip. As a result, the gasket is also free from the problem of detached or separated segments of flashes or burrs. In addition, there is no risk of the flashes or burrs interfering with the component parts within the unit casings because the flashes or burrs are formed outwardly of the inner sealing lip.
These features and advantages of the invention, as well as other features and advantages thereof, will become apparent from the following description.